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INFLUENCE OF PORE-WATER TENSION ON THE STRENGTH OF CLAY

The magnitude of the pore-water tensions and the change in strength on stress release are estimated theoretically for the range of pressures within which the sample remains fully saturated. Tests on samples of two clays consolidated in the triaxial apparatus under a wide range of pressure indicate that the limiting pore-water tension above which the sample ceases to remain fully saturated is related to the equivalent pore diameter. Above this limit the loss in strength on stress release is very marked. The experimental results also show the dramatic change in brittleness resulting from high pore-water tensions. A large reduction in total stress without a change in water content is sufficient to change the failure mechanism from a plastic failure with some strain-softening to a brittle failure in which the sample shatters. The significance of the results in relation to sampling and testing of soils for engineering purposes in briefly considered.